Argillites are highly compact sedimentary or slightly metamorphosed rocks that consist largely or wholly of particles of clay or silt but lack the fissility of shale or the cleavage characteristic of slate. Argillite is found at the Slatechuck argillite quarry on Slatechuck Mountain near Skidegate on the east flank of Graham Island in the Haida Guwaii of the North Coast of BC.